Most programs interact with the outside world in some way, whether it be
via a file, a network, a serial cable, or the console. Sometimes, as is the
case with networking, individual I/O operations can take a long time to complete.
This poses particular challenges to application development.

Boost.Asio provides the tools to manage these long running operations, without
requiring programs to use concurrency models based on threads and explicit
locking.

The Boost.Asio library is intended for programmers using C++ for systems
programming, where access to operating system functionality such as networking
is often required. In particular, Boost.Asio addresses the following goals:

Portability. The library should support
a range of commonly used operating systems, and provide consistent behaviour
across these operating systems.

Scalability. The library should facilitate
the development of network applications that scale to thousands of concurrent
connections. The library implementation for each operating system should
use the mechanism that best enables this scalability.

Efficiency. The library should support
techniques such as scatter-gather I/O, and allow programs to minimise data
copying.

Model concepts from established APIs, such as BSD
sockets. The BSD socket API is widely implemented and understood,
and is covered in much literature. Other programming languages often use
a similar interface for networking APIs. As far as is reasonable, Boost.Asio
should leverage existing practice.

Ease of use. The library should provide
a lower entry barrier for new users by taking a toolkit, rather than framework,
approach. That is, it should try to minimise the up-front investment in
time to just learning a few basic rules and guidelines. After that, a library
user should only need to understand the specific functions that are being
used.

Basis for further abstraction. The library
should permit the development of other libraries that provide higher levels
of abstraction. For example, implementations of commonly used protocols
such as HTTP.

Although Boost.Asio started life focused primarily on networking, its concepts
of asynchronous I/O have been extended to include other operating system
resources such as serial ports, file descriptors, and so on.